Micronization of the officinal component emodin via the SEDS process through prefilming atomization

The micronization of emodin in a mixed solution of dichloromethane and methanol by the Solution Enhanced Dispersion by Supercritical Fluids through Prefilming Atomization (SEDS‐PA) process has been successfully performed. Morphologies and particle sizes (PSs) of the emodin microparticles were analyzed by scanning electron microscopy. The results of micronization show that the acicular or rod‐like emodin crystals with PSs of about 3‐10 µm wide and 100‐300 µm long have successfully been micronized to needle‐like, rod‐like, twisted fiber‐like and coalesced net‐like microparticles with PSs of about 0.1‐1.0μm wide and 2‐40μm long by the SEDS‐PA process. The effect of technological conditions on micronization has been studied. With the increase of initial solution concentration and temperature, the PSs of emodin microparticles increase. With the increase of solution flow rate and pressure, the PSs of emodin microparticles decrease. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization of micro particles of sulindac using rapid expansion of supercritical solution

In pharmaceutical industry, many drugs exhibit poor solubility in biological fluid. Solubility of drugs affects on the rate of dissolution and bioavailability in biological fluids. The bioavailability of drugs can be enhanced by decreasing the drug particle size. In this study, sulindac was micronized via rapid expansion of supercritical solution (RESS) where CO2 was used as a solvent. The experiments were conducted to investigate the effect of the extraction pressure and temperature (140–230 bar and 40–60 °C), collection distance (1–10 cm), effective nozzle diameter (450–1700 μm) and nozzle length (2–15 mm) on the size and morphology of the sulindac particles. The size and morphology of the precipitated particles were monitored by scanning electron microscopy (SEM). The particle size of intact sulindac particles was about 33.03 μm, while the average particle size of the micronized sulindac particles was between 0.76 and 8.02 μm based on different experimental conditions. Additionally, the different morphology of the micronized particles was observed like needle, rectangular, quasi spherical and irregular form while the morphology of the intact particles of sulindac was rectangular and irregular.     

Structural and catalytic properties of Cu2S microrods grown on a three‐dimensional substrate

We present a facile solution‐phase method for the synthesis of Cu₂S microcrystals with rod‐like morphologies by the reaction of sulfur with three‐dimensional substrate copper foam in a mixed solvent of ethylene glycol and deionized water. The lengths of Cu₂S microrods are between 80 and 150 μm and the diameter is among 3 to 8 μm. Monodisperse Cu₂S microrods self‐assemble into echinus structure. The samples were characterized by X‐ray powder diffraction and scanning electron microscopy. Energy dispersive X‐ray spectroscopy was further used to testifiy the purity of Cu₂S. Catalysis performance proved that the obtained Cu₂S materials possess superior catalytic efficiency on methylene blue with the assistance of H₂O₂. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation of monodispersed aragonite microspheres via a carbonation crystallization pathway

Monodispersed calcium carbonate microspheres were prepared by carbonating a calcium acetate aqueous solution with CO₂ gas at a high pressure of 40 bar and a high temperature of 80 °C after 60 minutes of reaction. The products were characterized by X‐ray powder diffraction (XRD) and scanning electron microscopy (SEM), respectively. The XRD pattern showed that the crystal polymorph of the as‐prepared monodispersed microspheres was aragonite. The SEM images also displayed needle‐like aragonite self‐organized into microsphere superstructure with diameters ranging from 5 to 15 μm. Analysis of the formation mechanism of the calcium carbonate microsphere superstructure revealed that the rod‐dumbbell‐sphere morphogenesis mechanism along with the phase transformation of vaterite to aragonite was responsible for the growth of the monodispersed aragonite microspheres. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of strontium carbonate rods and hierarchical branches in the presence of two organic additives

In this paper, strontium carbonate (SrCO₃) crystals have been synthesized in the presence of two organic additives, including sodium citrate and hexamethylenetetramine (HMT). Scanning electron microscopy, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, X‐ray powder diffractometry and selected area electron diffraction (SAED) were used to characterize the products. The results indicate that SrCO₃rods with the ratio of length to diameter about 20 are obtained in the aqueous solution containing sodium citrate. While polycrystalline SrCO₃ hierarchical branches with about 10 μm length are produced by using HMT.The possible formation mechanism of the SrCO₃crystals obtained in above two systems is discussed, which can be interpreted by particle‐aggregation based non‐classical crystallization laws. Sodium citrate and HMT may direct the formation of SrCO₃ rod‐like or branch‐like structures by adsorbing onto certain facets of SrCO₃ crystals. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A study of the growth process of Co3O4 microcrystals synthesized via a hydrothermal method

Pure Co₃O₄ microcrystals were prepared by a hydrothermal method from Co(NO₃)₂·6H₂O and urea solution, and the effect of thermal treatment time on the growth of Co₃O₄ microcrystals was studied by X‐ray diffraction (XRD), scanning electron microscopy (SEM), Raman and UV‐Vis absorption spectra. The results show that with the thermal treatment time increases from 2 h to 12 h, the shape of as‐prepared Co₃O₄ microcrystals changes from the hedgehog sphere‐like to the as‐cubic one that were stacked by lots of lamella, and finally cubes, and then longer time treatment will only lead to the size growth and agglomeration of particles. In conclusion, the cubic Co₃O₄ microcrystals of uniform size (∼6 μm) are synthesized via a 12‐h thermal treatment. Moreover, the synthesis mechanism has been studied.     

Hydrothermal synthesis and formation of 4ZnO·B2O3·H2O whiskers via a new route

4ZnO·B₂O₃·H₂O whiskers were prepared from 2ZnO·3B₂O₃·3.5H₂O under hydrothermal process at 160 °C for 10 h. The synthesized product was characterized by XRD, SEM, TG‐DSC and FT‐IR. SEM results showed that the synthesized 4ZnO·B₂O₃·H₂O whiskers' length was about 3–10 μm and the diameter was 0.2–0.3 μm. Further study on the whiskers' growth process and mechanism showed that the formation of the whiskers went through three stages and the morphology of 4ZnO·B₂O₃·H₂O changed from irregular particles to rod‐like structures and finally to whiskers. The variation of the morphology of the 4ZnO·B₂O₃·H₂O whisker with the concentration of the starting material was investigated. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optimization of process parameters by Taguchi method in the recovery of lactose from whey using sonocrystallization

Anti‐solvent crystallization of lactose in the presence of ultrasound will reduce crystal size and the level of agglomeration as compared to the commercial cooling crystallization. It offers a potential route to enhance the physical properties as well as the rapid recovery of lactose. Since lactose recovery itself can reduce biological oxygen demand of whey by more then 80%, recovery of lactose from dairy waste stream (whey) solves the problems of dairy industries by improving economics of whey utilization and pollution reduction. In the present study, recovery of lactose from partially deproteinated whey using an anti‐solvent (acetone) by sonocrystallization was optimized for finding the most influencing operating parameters; such as sonication time, anti‐solvent concentration, initial lactose concentration in the whey and initial pH of sample mixture at three levels using L₉‐orthogonal method. The responses were analyzed for recovery of lactose from whey. The anti‐solvent concentration and the sonication time were found to be most influencing parameters for the recovery of lactose and the recovery of lactose was found to be 89.03% at the identified optimized level. The crystal size distribution of recovered lactose was found to be narrower (2.5 – 6.5 μm) as compared to the commercial lactose crystals (3.5 – 9.5 μm). (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation of Li2CO3 by gas‐liquid reactive crystallization of LiOH and CO2

A spinning disk reactor (SDR) was used in this research to prepare Li₂CO₃ by gas‐liquid reactive crystallization of LiOH and CO₂. It was found that the end pH value of the above reaction should be controlled within the range of 9.0‐9.5 to obtain a high yield of Li₂CO₃. The effects of operational parameters (including the temperature, the concentration of LiOH solution, the rotation rate of the spinning disk, the circulation rate of LiOH slurry, the flow rate of CO₂ and the ultrasound field) on the particle size and the yielding rate were investigated by an orthogonal experiment. The results show the significant factors influencing the particle size are the ultrasound field, the temperature and the flow rate of CO₂. As for the yielding rate, the temperature, the concentration of LiOH solution and the flow rate of CO₂ exert obvious impacts, while the effects of ultrasound field and the rotation rate of the spinning disk are limited. The SEM images show the Li₂CO₃products are flower‐like particles, which are composed of plate‐like primary crystals. The size analysis shows the volume mean particle size of the Li₂CO₃products ranges 37‐90 μm depending on the various experimental conditions. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of forced solution flow on lysozyme crystal growth

In order to study quantitatively the effects of forced solution on crystal growth, we designed a new set of experimental equipment, in particular, a microchannel mixer was used as crystallization container so that the consumption of protein samples was much reduced and thus an exact syringe pump could be used for precise control of the flow rates. Since the mixer's section was designed to be rectangular, the solution velocity in its center was steady and constant, and thus repeatable experiments were facilitated. Experimental results showed that the effects of forced solution on protein crystal growth were different under different levels of supersaturation, and new results were obtained for cases of high supersaturation. When the supersaturation is σ = 2.3, with increasing flow rates the growth rates of the lysozyme crystal's (110) face hardly change when the flow rates are lower than 1300 μm/s, and decrease quickly afterwards. When the flow rate reaches 2000 μm/s, the crystal nearly ceases to grow. When the supersaturation is σ = 2.7, with increasing flow rates the (110) face growth rates increase at the beginning then reach the maximum values at 1700 μm/s – 1900 μm/s and decrease afterwards, approaching zero or so when the flow rate reaches 12000 μm/s. The higher the supersaturation, the larger the flow rate at which the crystal ceases to grow. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural and optical properties of vapour‐etching based porous silicon

The structural and optical properties of porous silicon (PS) layers prepared by Vapour‐Etching (VE) of moderately and heavily boron‐doped Si substrates are investigated. The VE technique produces rough PS layers that are essentially formed of interconnected cluster‐like structures. Optical investigations indicate that this surface roughness enables the PS layers to be used as antireflection coatings in silicon based devices. These optical characteristics are investigated by optical reflectivity and light scattering. The local chemical state and the microstructure of the PS layers are studied by electron energy loss spectroscopy (EELS) in transmission electron microscopy (TEM), and are correlated to the red photoluminescence (PL). TEM studies point out that the cluster‐like interconnected structures are composed of luminescent nanocrystallites. PL measurements display that both quantum confinement and surface passivation determine the electronic states of the silicon nanocrystallites. The complex dielectric function is calculated from the experimental single‐scattering distribution spectrum using a Kramers Kronig analysis. The first resonance peak in the imaginary part is observed at 2.3 eV; two other broadened features appear at 4.7 and 8.8 eV. The latter is generally related to an interface plasmon resulting from the silicon‐silicon oxide interface. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Studies on fabrication of urchin‐like WO3·H2O hollow spheres and their photocatalytic properties

Urchin‐like tungsten oxide hydrate (WO₃ · H₂O) hollow spheres were successfully synthesized via a self‐sacrifice template method at low temperature. The effects of reaction parameters on the preparation were studied in solution. The growth mechanism was also proposed on the basis of experimental results. In addition, the acid amount and temperature have important effects on size control of the as‐obtained samples. The achieved nanoarchitectures have typical diameters of 4–6 μm with nanoflakes of several nanometers at surface. Crystal structure, morphology, and composition of final nanostructures were characterized by X–ray diffraction (XRD) and scanning electron microscopy (SEM). Degradation experiments of organic contaminant were also performed on samples of hollow spheres and walnut‐like structures under visible‐light illumination. Hollow sphere sample exhibited better photocatalytic capability than walnut‐like sample. Possible mechanism was studied for WO₃ · H₂O assisted photocatalytic degradation of organic contaminant under visible light.     

Impact of agglomeration on crystalline product quality within the crystallization process chain

The quality of crystalline products, defined by e.g. purity or crystal size distribution (CSD), is primarily dominated by crystallization conditions but influenced by further downstream processes like solid‐liquid separation and drying also. Through uncontrolled agglomeration within the crystallization process chain the purity or CSD can be negatively affected. Therefore, in context of process optimization, missing knowledge of the impacts on the final product can lead to product batches out of specification. To increase the understanding of agglomeration and to provide insight into the relevance of holistic process optimization the agglomeration behavior of L‐alanine crystals is exemplarily quantified over the crystalline process chain. For the quantification the agglomeration degree (Ag) and the agglomeration degree distribution (AgD) are determined. The results show that the product quality achieved after crystallization is significantly affected by agglomeration during drying. Especially if washing after solid‐liquid separation is omitted, a broadening of the CSD is observed. Moreover, the evaluation by the AgD indicates that the final product can be ‐ despite similar characteristics of the CSD ‐ highly different. Consequently, it can be concluded that the characterization of the product quality by the CSD alone is insufficient and the quantification of agglomeration is essential for process optimization.     

Simple extraction‐solvothermal synthesis of single‐crystalline silver microplates

Single‐crystalline silver microplates, with average edge length of about 1.5 μm and thickness of 100 nm, have been synthesized by a simple extraction‐solvothermal method. Samples were characterized in detail by X‐ray diffraction (XRD), field‐emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM) and High‐resolution transmission electron microscopy (HRTEM) technologies. Extractant primary amine N1923 can also act as reducing agent. It has been found that microstructure of the silver can be controlled by the n‐octanol during the solvothermal treatment. Based on a series of experimental analysis, the possible formation mechanism of these microplates was discussed briefly. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of SrMnO3 powders with different morphologies by hydrothermal method

By using two different reagents as the starting materials, SrMnO₃ crystallines with two different morphologies rhombus‐like and rod‐like, have been directly synthesized by hydrothermal conditions. The effects of the hydrothermal parameters on the quality of the SrMnO₃ samples were given for the fist time. And a preparative mechanism for the formation of different morphologies using different reagents during the hydrothermal reaction has been discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Precipitation of nesquehonite from homogeneous supersaturated solutions

The homogeneous (unseeded) precipitation of nesquehonite (MgCO₃·3H₂O) was studied over the temperature range of 10‐40 °C. Precipitation was triggered by the supersaturation created by mixing MgCl₂ solution (0.5‐1.5 M) with Na₂CO₃ solution in the same concentration range. The Meissner's method was adopted in the calculation of supersaturations during the MgCl₂‐Na₂CO₃ reaction to monitor the precipitation. Solids were identified using X‐ray diffraction (XRD) analysis and scanning electron microscope (SEM) images. In the temperature range of 10‐40 °C, MgCO₃·3H₂O with needle‐like or gel‐like morphology was precipitated. It was seen that the length, width and surface smoothness of the particles changed with reaction temperature and supersaturation. The supersaturation (S) was in the range of 1.09‐58.68 during titration of Na₂CO₃ solution. The dimension of the crystals increased with longer addition time (or lower initial concentration of reactant) at the same temperature. Slower addition via titration of 2 h followed by 2 h of equilibration at 40 °C proved successful in producing well developed needle‐like MgCO₃·3H₂O crystals of 30‐50 μm long and 3‐6 μm wide. MgCO₃·3H₂O obtained were calcined to produce highly pure magnesium oxide (MgO) at 800 °C. The morphology of MgO was similar to that of their corresponding precursors. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A direct suppression of green band emission of ZnO particles by adjusting the volume fraction of ethanol in reaction solutions

ZnO particles were successfully prepared by one step CTAB‐assisted hydrothermal method with different volume fraction of ethanol‐water mixture solution. The formed thorn‐ball like ZnO particles have an average size of 1 ∼ 2 μm in diameter. XRD result shows a hexagonal wurtzite structure and higher crystallinity. Room‐temperature photoluminescence shows a strong and dominated peak at ∼383 nm with a green emission at ∼510 nm. The intensity ratio between the UV and green emission increased from 1.31 to 7.53 when the volume fraction of ethanol was changed from 0% to 50%, which shows a direct suppression of structural defects just by adjusting the ethanol fraction in reaction solutions. The possible growth and luminescence mechanisms for thorn‐ball like ZnO particles are discussed.     

Morphology‐photocatalytic properties‐growth mechanism for ZnO nanostructures via microwave‐assisted hydrothermal synthesis

ZnO nanostructures with various morphologies including rod‐like, sheet‐like, needle‐like and flower‐like structures were successfully synthesized via a fast and facile microwave‐assisted hydrothermal process. Reaction temperature, reaction time and the addition of NaOH were adjusted to obtain ZnO with different morphologies. Scanning electron microscopy(SEM), transmission electron microscope(TEM), X‐ray diffraction (XRD) and ultraviolet spectrophotometer (UV) were used to observe the morphology, crystal structure, ultraviolet absorption and photocatalytic activity of the obtained ZnO. The results indicated that growth rate of ZnO nanostructure along [001] direction was more sensitive to temperature compared with those along [101] and [100] directions. The competition between anionic surfactant and OH⁻ played an important role in the formation of ZnO with various morphologies. Flower‐like ZnO had better ultraviolet absorption property and excellent photocatalytic activity than ZnO in the other morphologies. On the basis of the above results, a possible growth mechanism for the formation of ZnO nanostructures with different morphologies was described.     

Growth of Ba2Re(Y,Pr)Ru1‐xCuxO single crystals in a high temperature solution drop using an infrared imaging system

Infrared imaging furnace was used to grow single crystals of Ba₂YRu_1‐xCu_xO₆ and Ba₂PrRu_1‐xCu_xO₆ using high temperature solutions of PbO‐PbF₂ in the form of a bubble attached to the feed rods. Several small crystals were found deposited on the cooler portions of the sintered rod as well as in the drop like portion at the end of the rod. These crystals were collected and the morphology, microstructure and magnetic properties were studied. The details of these investigations are presented. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nucleation kinetics of the formation of low dimensional calcium sulfate dihydrate crystals in isopropyl alcohol medium

Calcium sulfate dihydrate, constituted as uniform crystals of low dimensions, is a potential biomaterial for clinical applications like bone graft substitution and drug delivery. In this work, isopropyl alcohol has been used as a solvent to obtain low dimensional calcium sulfate dihydrate crystals from calcium nitrate ‐ sulfuric acid system. Reactants in 0.5 molar concentration at ambient conditions generated uniform rod‐shaped crystals of length 3–5 µm. Analysis using X‐ray Diffractometry and Fourier Transform Infrared Spectrometry showed the material to be well crystallized, phase‐pure calcium sulfate dihydrate. The nucleation kinetics has been studied by observing the induction time of phase formation in solutions of millimolar concentrations through turbidimetry at 300 K. The data have been analysed using classical nucleation theory to deduce parameters like interfacial tension (or surface free energy), nucleation rate and critical radius. The surface free energy obtained (5.6 mJ/m²) is comparatively lower than that reported for aqueous precipitation, which could be attributed to the presence of isopropyl alcohol. On escalating the supersaturation ratio, the nucleation rate drastically increased and the critical radius decreased exponentially. Particles formed at supersaturation 1.39 showed a monomodal distribution centered at 8.2 nm in Dynamic Light Scattering analysis. Comparable particle sizes were obtained in Transmission Electron Microscopy.